Workable polyamides by blending with inorganic thiocyanates

ABSTRACT

POLYAMIDES CAN BE TAILORED TO HAVE MORE WORKABLE PROPERTIES BY BLENDING WITH A MINOR PORTION OF AN INORGANIC THIOCYANATE SUCH AS SODIUM OR POTASSIUM THIOCYANATE. WITH THE EXCEPTION OF AMMONIUM THIOCYANATE, WHICH HAS THE OPPOSITE EFFECT ON MELT VISCOSITY, THE BLENDS RAISE MELT VISCOSITY, AND LOWER THE NORMAL FREEZING POINT. INDIVIDUAL PHYSICAL PROPERTIES OF THE EXTRUDED OR MOLDED POLYAMIDE BLEND REMAIN THE SAME OR ARE IMPROVED, EXCEPT WITH AMMONIUM THIOCYANATE WHICH REDUCES TENSILE STRENGTH AND ELONGATION.

United States Patent 3,577,392 WORKABLE POLYAMIDES BY BLENDING WITH INORGANIC THIOCYANATES Rajindar K. Kochhar and Bert H. Clampitt, Overland Park, and Ronald E. Gilbert, Shawnee Mission, Kans., assignors to Gulf Research & Development Company, Pittsburgh, Pa. N0 Drawing. Filed Oct. 31, 1968, Ser. No. 772,396

Int. Cl. C08g 20/38 US. Cl. 260-78 3 Claims ABSTRACT OF THE DISCLOSURE Polyamides can be tailored to have more workable properties by blending with a minor portion of an inorganic thiocyanate such as sodium or potassium thiocyanate. With the exception of ammonium thiocyanate, which has the opposite eifect on melt viscosity, the blends raise melt viscosity, and lower the normal freezing point. Individual physical properties of the extruded or molded polyamide blend remain the same or are improved, except with ammonium thiocyanate which reduces tensile strength and elongation.

BACKGROUND OF INVENTION This invention relates to a composition and method of improving processability and melt characteristics of polyamides by blending a major portion of the polyamide with a minor portion of an inorganic thiocyanate in conventional blending apparatus.

Many attempts have been made to improve melt viscosity of polyamides without sacrificing other properties, such as processability. Melt viscosity can be improved by post polymerization to increase molecular weight, but such treatment has always resulted in a product which is melt-unstable on usual plastic forming equipment such as extruders with the result that formed products show a wide variation in physical properties. Nucleating agents like talc or calcium carbonate do not materially affect the workability of polyamides.

SUMMARY Blending a major portion of a polyamide with a minor portion of an inorganic thiocyanate allows a blended composition which can be tailored to have properties which make it more workable than the unblended polyamide. The blend can be made in conventional plastic material forming apparatus. Blends prepared by using alkali metal thiocyanates raise melt viscosities, lower freezing points, and improve overall physical properties. Ammonium thiocyanate lowers melt viscosities without changing freezing points. Thus the processing properties of any given polyamide can be altered by making the appropriate polyamide-thiocyanate blend.

PREFERRED EMBODIMENTS The blends of this invention can contain from about 99.99 to 80% by weight, based on the weight of the entire blend, of polyamide and, correspondingly, about 0.01 to 20% by weight of inorganic thiocyanate. A more preferred blend would be about 0.5 to 10% by weight of thiocyanate, and the preferred blend contains about 1 to 5% by weight of inorganic thiocyanate. Any of the inorganic thiocyanates, such as the alkali metal thiocyanates and ammonium thiocyanate can be used. Preferred alkali metal thiocyanates are sodium and potassium thiocyanate. Any polyamide can be used. Preferred polyamides are polycaprolactam, polyhexamethylene adipamide, poly(12- aminododecanoic acid), and polyhexamethylene sebacamide; most preferred is polycaprolactam.

The blends of this invention are prepared by simply blending polyamide with the inorganic thiocyanate. For example, dry inorganic thiocyanate can be added to molten polyamide and blended in conventional thermoplastic blending apparatus. The preferred method is to immerse the polyamide in a solution of the inorganic thiocyanate so that the solution impregnates the polyamide. Then the impregnated polyamide is blended in the molten state in conventional thermoplastic material blending apparatus whereby the inorganic thiocyanate becomes uniformly distributed throughout the polyamide. The polyamide can be vacuum dried before immersion in the thiocyanate solution, preferably 'at a temperature between about 50 to C. The impregnated polyamide is generally dried in a vacuum oven and blended at a temperature above the melting point but below the decomposition temperature of the polyamide for about 1 minute to about 1 hour, preferably it is dried at a temperature between about 50 to 100 C. and blended at a temperature of between about C. and 350 C. for about 2 minutes to /2 hour.

The uses of these polyamide-thiocyanate blends are the same as for the uses known in the art for the polyamides. Since these blends are more workable, they are more easily extruded, and can be also molded. Examples of possible uses are in extruded tubes, sheets, films, fibers and as molded parts. Oriented film could be broken down into fibers by processes known in the art.

The term polyamide, for purposes of this application, includes copolymers containing predominately amide comonomers and mixtures of polyamides or polyamide copolymers.

Preferred embodiments are illustrated by the following examples.

The following tables present data on polyamide-thiocyanate blends prepared by vacuum drying polyamide chips at 55 C.; then immersing the polyamide chips in an aqueous solution of the thiocyanate so that the chips are impregnated with the given parts by weight of thiocyanate, determined by the difference in weight before and after immersion; then drying the impregnated chips in a vacuum oven at 55 C. for 24 hours; then blending the impregnated chips in a Brabender Plasticorder for 10 minutes under a current of dry nitrogen at a temperature of 235 to 240 C. for polycaprolactam, polyhexamethylene sebacamide, and poly(12-aminododecanoic acid), and at a temperature of 275 C. for polyhexamethylene adipamide. Finally the blends are tested for the properties shown in Tables 1, IA, II, and III.

TABLE I.PHYSIOAL PROPERTIES OF NYLON THIOOYANATE BLENDS Nylon Thiocyanate Tensile Flex- Shore Solu- Melt stability Parts Parts Melt strength, p.s.i. ural D 121011 I. at by flow still hard- VlS- 235 C., 6 9 12 15 Type weight Type weight index Yield Break ness ness cosity g. min. min. min. min.

Nylonfi) (NX3013, Gulf Oil 100 14.82 5,465 6,413 226,274 76 2.76 0.4

orp. D 99 NaCNS 1 8.07 8,570 12,517 170,890 78 2.33 1.9 97 NaONS 3 5.13 7,520 12,484 141,705 81 2.43 1.8 5.62 5.50 5.71 5.54 95 NaCNS 5 3.89 6,411 11,580 132,764 79 2.48 2.4 99 KCNS 1 9.35 9,318 10,321 204,198 82 2.53 1.3 97 KONS 3 8.76 9,081 10,450 176,294 79 2.58 1.5 8.76 8.53 8.61 8.79 95 KCNS 5 6.60 8,320 10,630 145,850 81 2.58 2.0 99 NH4CNS 1 79.7 76 100 9.52 78 99 NACNS 1 3.52 97 NAONS 3 1.65 95 NACNS 5 0.68 99 KCNS 1 3.51 97 KCNS 3 2.93 95 KCNS 5 0.78 99 NHrONS 1 123 97 NH4ONS 3 HIGH 1 Decigrams per minute at 235 042,160 g.; 3 min. temperature equalization time.

B 1% solution in 90% formic acid. 3 Initial tension (gms.), a measure of the melt strength. 4 M.F.I. after heating the given number of minutes at 235 0.

TABLE IA.PHYSICAL PROPERTIES OF NYLON THIOCYANATE BLENDS Nylon Thiocyanate Tensile strength,

Melt p.s.i. Parts by Parts by flow Flexural Tensile LT. 9 Shore D" Type Weight Type weight index 1 Yield Break stifiness impact (gms.) Hardness Nylon 66 (Du Pont Zytel-42) 100 CONTROL 10, 304 232, 920 112. 6 1. 3 82 Nylon 66 99 NHiCN S 1 10, 364 236, 524 81. 4 2. 6 82 D 97 NHqONS 3 209, 62 Fast 82 99 KCN S 1 8, 453 196, 69 92. 3 2. 81 97 KCNS 3 7, 853 207, 571 78. 6 Fast 81 N 100 CONTROL 5, 024 152, 071 62. 7 74 N 99 NH4CNS 1 827 120, 628 81.8 1.3 77 97 NH4CNS 3 5, 642 767 65. 6 Fast 77 99 KCN S 1 11, 219 135, 388 108. 2 0. 9 78 97 ON 3 7, 773 127, 001 116. 6 Fast 78 Nylon 12 (Olin 1203). 100 C ONTROL 7, 108 116, 745 104. 73 99 NHrON S 1 7, 111 126, 303 73. 3 3. 1 72 97 NHrGNS 3 396 92, 916 55. 9 0. 4 71 99 CNS 1 10, 866 127, 330 173.0 2. 8 75 97 KCNS 3 10, 046 71, 623 94. 4 1. 2 64 1 Deeigrams per minute, nylon 66 at 275 0.; nylon 610 at 235 C. and nylon 12 2 Initial tension draw at /min.

Viscosity at (poises) Composition, Melt fiow percent dex, 10 dynes/ thiocyanate g./10 mm. cm. 1 ,000 see.- 13.89 sec.-

The effects of blends on physical properties can be seen in the tables. Note the melt flow index for nylon 6 dropped from about 14.8 with no thiocyanate to about 3.9 with 5 percent NaCNS. [Both tensile strength and elongation increased with the addition of alkali metal thiocyanate. The break tensile rose from about 6,400 to about 11,500 with the addition of 5 percent NaCNS. Elongation (not shown in the tables) went from percent with no thiocyanate to 120 percent with 2.5 percent sodium thiocyanate. Melt strength, as shown by initial tension, also increases and so does the melt stability.

Ammonium thiocyanate, as can be seen in the table, can be used to lower melt viscosity, tensile strength, elongation and stillness. Thus, the thiocyanates can be used to tailor the polyamide properties upward or downward.

at C. A dead weight of 2160 g. was employed in each case.

The following is a list of test methods for the various properties.

Melt flow index ASTM D1238-65T FR-R. Stiifness s ASTM D747-63. Tensile ASTM D6 38-64T.

DIFFERENTIAL THERMAL ANALYSIS (DTA) OF THIOCYANATE CONTAINING POLYAMIDES One method of evaluating the eifect of additives on crystal and other properties of the resins is through the use of differential scanning calorimeter. Any changes in the physical properties are likely to show up in their crystallization behavior and hence the melting and freezing curves of the polymers. Melting and freezing characteristics of these blends are given in Table III.

An interesting feature of DTA curves is that with increasing concentration of thiocyanates in the blend there is a continued suppression of the freezing point. In the thiocyanate blends a dilferentiation can be made between those prepared with alkali metal compounds on the one hand and ammonium salts on the other. Alkali metal thiocyanate-nylon compositions show a deep depression in the melting temperatures and those containing small amounts of ammonium thiocyanate with nylon are not much different from the base resin in this respect.

3. The article of manufacture of claim 1 wherein the polyamide is polycaprolactam.

TABLE III.THERMAL ANALYSIS OF NYLON 6 BLENDS Sample Scan Melting temperature, C. Freezing wgt., rate, Cooling range,

Sample mg. /min. Minor Shoulder Major rate C.

Spl. 1 10. 10 167-146 100% Spl. 2 10. 05 181% 166-147 Spl. 1 10.00 162 nylon NBCNS 10' 10 174 154-147 nylon 6, KCNS 10' 169 147 Spl. 1- 10.00 139. 6

nylon NaCNS SP1 10 06 1M 141 Spl. 1- 10. 04 132 nylon KCNS m 06 157 132 Spl. 1 10.04 129 nylon NaCNS SPL mm 155 129 Spl. 1 9. 98 162. 5-153 99% nylon 6, 1% NHlCNS SP1. 2"." 10 00 182 164-155 References Cited UNITED STATES PATENTS 2/1944 Dwyer 26078 8/ 1945 Ki'lng 260-78 6/1951 Walker 26078 2/ 1958 Steiger 26078 1/1959 Hubbard et a1. 26078 HAROLD D. ANDERSON, Primary Examiner U.S. Cl. X.R.

26045.9R, 78A, 78L, 788, 788C 

